Transducer



July 4,1944. H. B. SHAPIRO TRANSDUCER Filed March 26, 1942 2 Sheets-Sheet l FIG. 2

INVENTOR. HARDY B. SHAPIPO y 9 H. B. SHAPIRO 2,353,089

TRANDUCER Filed March 26, 1942 2 Sheets-Sheet 2.

7 INVENTOR.

HARRY B. SHAPIRO WMWK Patented July 4, 1 944 UNITED STATES PATENT OFFICE TRANSDUCER Harry B. Shapiro, Willoughby, Ohio, asslgnor to The Brush Development Company, Cleveland,

Ohio, a corporation of Ohio Application March 26, 1942, Serial No. 436,230

18 Claims. (01. 171-327) This invention relates to transducers and, more particularly to transducersof the type wherein a piezo-electric element is utilized for converting electrical energy into mechanical movements or mechanical stresses into electrical potentials.

Transducers of the general type to which this invention pertains are exemplified by the Sawyer Reissue Patent 20,680 and by the Williams Patent It is an object of the invention to provide housing means, for piezoelectric units, that shall be waterproof, sturdy and capable of resisting rough handling in use.

Another object of this invention is to provide piezoelectric crystal unit housing means that shall require the minimum number of separate parts.

Another object of the invention is to provide housing means, of the type described, that shall be substantially unaffected by changes in barometric pressure.

Another object of the invention is to provide hermetically sealed housing means, of the type described, such that mechanical movement may be transmitted to or from a crystal element contained therein without the necessity of resorting to sealing means for the drive rod such as are disclosed in the Williams patent.

Another object of the invention is to provide a sealed piezoelectric unit cartridge that may be utilized as a replacement part in apparatus such as phonograph pickups, loud speakers, microphones, oscillographs and the like.

Another object of the invention is to provide electrostatically shielded housing means of the type described.

Another object of the invention is to provide housing means, of the type described, capabl of accommodating piezoelectric "Bimorphs that vary slightly in thickness.

' A still further object of the invention is to provide housing means, of the type described, that shall'flrmly hold a piezoelectric "Bimorph in fixed position yet shall impose minimumrestraint upon vibratory movement thereof. I In a preferred embodiment of the invention,

the housing takes the form of a U-shaped, rigid frame, hermetically sealed by a cover-sheet of metal foil that is folded around the open end of the frame and cemented to its opposite faces. A rectangular piezoelectric Bimorph is mounted within the frame with its faces parallel to the foil cover-sheet, three comers of the crystal "element I being clamped to the inner walls of theframe and the free corner extending toward the spaced apart arms thereof.

' appended claims.

is intended to embrace all three-sided and/or open ended frames, irrespective of their contour, and whether or not the arms thereof converge, diverge or are parallel.

For the purpose of transmitting movement to or from the free corner of the Bimorph, small driving pads of semi-resilient or non-resilient material, such as hard rubber, Bakelite or the lke, are aflixed, respectively, to the opposite surfaces of the said corner, which pads contact the inner surface of the cover-sheet. The free corner, therefore, may be clamped, through the covering, to an appropriate motion-transmitting mechanism, such as a rod or a stylus holder, without disturbing the continuity of the cover-sheet or breaking the hermetic seal afforded thereby.

'The fold of the cover-sheet, between the drive pads and the adjacent ends of the U-shaped frame, may be crimped flat to reduce its stiffness.

The novel features characteristic of the invention are set forth with particularity in the The invention itself, however, both as to its organization and its method of operation, together .with additional objects and advantages thereof, will be understood best from the following description of a specific embodiment, when read in connection with the accomcomplementary U-shaped constituents of the housing frame;

Figure 4 is a vertical cross-sectional view of a frame element taken along a line corresponding to the line IV--IV in Figure 2;

Figure 5 is a plan view of a metal foil coversheet;

Figure 6 is a view in perspective of a piezoelectric cartridge, constructed according to the invention, exemplifying the mode of applying mechanical force to, or deriving mechanical movement from the crystal unit, and

Figure 7 is a vertical cross-sectional view of the device, taken along a line corresponding to the line VII-VII in Figure 6.

In all figures of the drawings, identical elements are similarly designated.

Referring now to Figures 1, 2, and 3 of the drawings a preferred embodiment of the invention comprises a U-shaped housing constituted by two U-shaped elements designated generally by the numerals I and 3 disposed in matching contact throughout their extent, the contacting faces of the said elements, respectively, being provided with three complementary half-notches I, 1 and 8. The half-notches 5 and I are formed in the inner walls of the arms of the U-shaped elements and the half-notch i is formed in the closed end thereof. Projecting upward from the base of each half-notch is a small hemispherical protuberance ll. These protuberances will be referred to hereinafter and their function explained in more detail. X

The half-notches, .when mated, are adapted to provide gripping sockets for the salient corners of a rectangular piezoelectric-unit II which, in Figure 1, is disclosed as being a Bimorph of the twister type such as is described in the Sawyer Reissue Patent 20,680. As is well-known to those skilled in the art, if three corners of a twister Bimorph" are held firmly by a mounting device, such as is shownin Figure 1, and potentials are applied to the central and outer electrodes afllxed to-the faces thereof, the free corner of the Bimorph" will flex, the direction of the bending being determined by the polarity of the applied potential.

Referring specifically to Figures 2 and 3, each of the U-shaped elements is provided with a pair .of complementary channels II and I! which,

Bimorph electrodes.

In the process of assembly of the improved piezoelectric unit cartridge three of the corners of a "Bimorph? are inserted, respectively, into the half-notches of one of the U-shaped elements and the leads therefrom are placed in the transverse channels I! and I1. Thereafter, a coating of water-proof cement is applied to the face of the U-shaped element and the mating element is superimposed thereon and pressed firmly into contact therewith. A jig or the like may be employed to hold the elements in engagement until the cement has firmly set.

Because of pressure exerted by the lie during the assembly process, the small protutsarances H rising from the floors, respectively, of the several half-notches are forced to a greater or less extent below the surfaces of the corner of the Bimorph" in contact therewith. Should the "Bimorph" vary slightly in thickness from a predetermined standard such variation will be compensated by greater or less penetration of the Drotuberancesinto the faces of the corners. The framework, therefore, is capable of accommodab ing crystals having slight variation in their thick ness while, at the same time, the three corners of the crystal are gripped firmly in the sockets constituted by the mating half-notches.

At this stage of the assembly or prior thereto, if desirable, a small block I! of material such as "Bakelite," hard rubber, Celluloid or the like is affixed to each face of the free comer of the ,"Bimorph the planes of the free ends of the blocks, respectively, lying approximately in the planes of the outer faces of the assembled frame. As

will hereinafter be explained, these blocks form links in a chain of mechanism whereby motion may be transmitted to the free corner of the "Bimorph or from the free corner thereof to assaose mented tautly to one face of the composite frame, is bent around the open end thereof and is cemented to the opposite face of the frame. The thickness of the foil may be of the order of .0005 of an inch. The open ends of the frame as well are cemented to the fold of the metal foil covering in contact therewith and the U-shapcd frame and the said covering, therefore, provide a hermetically-sealed container for the "Bimorph.

The appearance of the completed cartridge is exemplified by Figure 6 of the drawings from which it will be noted that the fold of the metal foil between the free end of the Bimorph and the arms of the U-shaped frame has been crimped. Such crimping, indicated by the nume'rals 21, 21, is for the purpose of increasing the flexibility of the end-fold in the covering which otherwise would be relatively stiff.

A drive link 29 or the like maybe clamped around the end of the cartridge to compress the cover-sheet 25 against the blocks 23 aillxed to the free comer of the "Bimorph" and to grip the free corner therebetween whereby motion may be transmitted to and from the said free corner without interrupting the continuity of the covering or breaking the hermetic seal afforded thereby. The manner in which the drive rod is clamped, effectively, to the free corner of the crystal may be discerned from Figure 7 of the drawings.

It will be noted from Figure 7 that the small protuberances H in a corner receiving socket slightly indent the corner of th Bimorph" inserted therein. Attention is also called to the fact that the flexible cover sheet I! is spaced away from the surfaces of the "Bimorph. The surface electrodes of the unit, therefore, need not be insulated nor need the Bimorph" unit itself be waterproofed unless such water-proofing is desired as additional protection. Furthermore, the metallic covering may be grounded to provide an electrostatic shield for the "Bimorph" or it may, if desired, be electrically connected to either the inner or outer electrode thereof externally or internally of the cartridge. In either event, substantially complete electrostatic shielding of the crystal unit is provided, which is a desirable feature in certain apparatus.

The U-shaped elements of the frame are made from insulating material, preferably hard rub ber, "Bakelite or the like or they may be composed of comic material that has a high dielectric constant.

The covering material may be of any suitable metal such, for example, as copper or aluminum, provided it be flexible in the neighborhood of the free end of the crystal and that it have reasonably high tensile strength.

The finished cartridge, either with or without the drive link 29 afllxed thereto, may be utilized as a replacement part in apparatus such as microphones, loud-speakers, vibration pickups, oscillographs and the like.

A cartridge constructed according to the invention is water-proof and is quite resistant to rough handling in use. Furthermore, by reason of its flexibility, the covering is free to give to some extent in response to barometric changes and thus to preclude the possibility of rupture.

This feature is very desirable because it enables.

maintenance of the hermetic sealing despite sudden changes in barometric pressure such as are encountered when piezoelectric apparatus is utilized on aircraft.

assaoee Also because of the fact that the hermetic seal is maintained despite changes in barometric imposing the slightest additional strain upon the crystal unit.

The outside foil cover may, if desired, constitute one of the connection terminals of the device. This is an advantage not attained with piezoelectric housing means such as were known previous to the invention.

Although a single specific embodiment of the invention has been shown and described it is not to be inferred that it is limited to housings for piezoelectric Bimorphs of the so-called twister type because, while still retaining the advantages secured by the invention, the housing may be suitably modifled, without invention, to accommodate crystal sections of other types such as benders.

It is also believed obvious that numerous other modifications will be apparent to those skilled in the art. The invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

What is claimed is:

1. A housing for a piezoelectric crystal unit, constituted by an open end frame having relieved portions wherein portions of said piezoelectric crystal unit are held, and a covering afflxed to both of the opposite faces thereof and extending entirely around the open end to define a closed container.

2. The invention set forth in claim 1, characterized in this, that the covering is flexible in the vicinity of the open end of the frame.

3. The invention set forth in claim 1, characterized in this, that the frame is U-shaped.

4. The invention set forth in claim- 1, characterized in this, that the covering is impervious to moisture and that it is sealed to the frame at all points of contact therewith.

5. The invention set forth in claim, 1, characterized in this, that the covering is metallic rectangular piezoelectric unit, and a rectangular piezoelectric unit disposed within the frame, at least two salient corners of said unit being held, respectviely, within said sockets.

8. The invention set forth in claim 7, characterized in this, that the faces of the piezoelectric unit, respectively, are disposed below and substantially parallel to the planes defined by the opposite faces of the U-shaped frame, and additionally characterized in this, that a flexible impervious covering is hermetically sealed to the faces of the frame and across the open end thereof to provide a closedcontainer.

9. The invention set forth in claim 7, characterized in this, that the U-shaped elements are made from electrically insulating material.

' 10. In combination, aplanar piezoelectric unit having a portion adapted to flex upon the application of electrical potential between the faces thereof or adapted to generate electrical potential in response to mechanical flexing thereof, ahermetically sealed container wherein said unit is mounted, the said container having at least two flexible walls spaced away from said unit, and means for conveying mechanical movement through both of said flexible walls of the container to or from the flexible portion of the unit.

11. The invention set forth in claim 7, characterized in this, that the faces of the piezoelectric unit, respectively, are disposed below and substantially parallel to the planes defined by the .opposite faces of the U-shaped frame, and additionally characterized in this, that a flexible metallic foil covering is hermentically sealed to the faces of the frame and across the open end thereof to provide a closed container.

12. In combination, a U-shaped frame, a piezoelectric crystal unit mounted within and enclosed by said frame, a free portion of said unit lying intermediate the arms of the frame adjacent the ends thereof, a moistureproof covering affixed to the faces of the frame and extending around the otherwise open end thereof to constitute a closed container, and means, including a part of the covering contiguous to the free portion of the piezoelectric unit, for transmitting mechanical forces between said free portion and exterior of the container.

13. The invention as set forth in claim 1, characterized in this, that the covering is metallic foil and is at all points spaced from said piezoelectric crystal. unit.

14. The invention as set forth in claim 1, characterized in this, that said frame includes passageway means for accommodating leads for the crystal unit.

15. The invention as set forth in claim 7, characterized in this, that the flexible impervious covering is metallic foil and is at all points spaced from the said piezoelectric unit.

16. The invention as set forth in claim 12, characterized in this that a portion of the moistureproof covering lying between the frame and the free portion of the piezoelectric unit is crimped to increase the flexibility of the said covering.

17. The invention as set forth in claim 1, characterized in this, that the covering is metallic foil and is grounded to establish the covering as an electrostatic shield for said crystal unit. 1 

